This invention relates generally to reinforced thermoplastic structures and methods of manufacturing such structures. This invention pertains particularly to compound composite structures in which thermoplastic resin material is bonded to a preformed composite reinforcing structure composed of fibers imbedded in thermoplastic resin material.
A method for producing solid rods by combining resin-impregnated, longitudinally extending, parallel strands or roving of fibers to form both the solid body or core of the rod as well as the outer layer of material consisting of the longitudinally extending, parallel fibers imbedded in plastic is disclosed by Leonard S. Meyer in U.S. Pat. No. 3,470,051. The Meyer patent mentions a method of applying an outer layer of parallel roving to the exterior of a prefabricated solid core. However, Meyer does not show a thermoplastic resin material bonded to a composite reinforcing structure. Meyer relies on a process of coating fiber strands with resin and later hardening the resin so that the fibers will be imbedded in the resin in longitudinally extending, exactly parallel relationship. Meyer discloses the use of an extrusion die which acts to guide resin covered fibers and combine them into a rod-like mass.
A method for encapsulating fibers in a collimated array within a thermoplastic resin matrix is disclosed by Baer et al in U.S. Pat. No. 3,635,879. The Baer process uses chopped glass strands in the preparation of capsules which may be used as feed stock for an extruder or molding apparatus. In U.S. Pat. No. 3,834,980, Hall discloses a method of extruding a coating of thermoplastic polymer over roving formed from fibrous strands. The Hall process is used to form pellets which may later be blended with thermoplastic and used in a molding process. A method of manufacturing plastic rods having fiber strands extending continuously throughout the length of the rod is shown by Koch in U.S. Pat. No. 2,625,498. The Koch method submerges a bundle of strands into a bath of thermosetting resin and then heats the bundle in a mold until the resin has completely set or cured. A granule consisting of lengths of glass roving coated with a molding plastic is described by Bradt in U.S. Pat. No. 2,877,501. The Bradt capsules are intended for use as a feed stock for an injection molding machine.
The prior art patents mentioned above do recognize the value of using fiber strands to reinforce plastics. However, the prior art does not show a method of adequately reinforcing thermoplastic resin to allow the manufacture of satisfactory parts and components. Particularly, the prior art does not show a satisfactory method of imbedding aligned fibers inside intricate part shapes. A satisfactory method of employing thermoplastic resins in the production of high strength plastic parts is not shown by the prior art. Also, the prior art does not show a simple method of imbedding continuous length fiber strands in a thermoplastic resin material using an extruder.